Bacterial Nanowires Could Revolutionize Electronics

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Physicists and biologists have teamed up to build a living
transistor -- an unusual kind of bacteria that produces long
stringy filaments outside its body that conduct electrons better
than some metals.

Scientists describe these filaments as a "living nanowire" that
could be a big step forward in merging biological systems and
electronic devices, leading to tiny organic super-batteries or
biological superconductors made for a fraction of the cost of
existing silicon-based chips.

The finding was reported in this month's issue Nature
Nanotechnology by a team at the University of Massachusetts
at Amherst.

The strings of nanowires, called pili, allow the bacteria
to get rid of electrons that are a byproduct of its digestive
process. Humans and animals get rid of electrons through
breathing, according to Mark Tuominen, professor of physics at
UMass and lead author of the paper. But bacteria living in
anaerobic zones don't have oxygen to carry the electrons. Each
one of these spaghetti-like strands is 10 to 20 times longer than
the bacteria itself, according to Tuominen.

The single-celled Geobacter sulfurreducens bacteria was
discovered in the 1980s in the oxygen-starved mud beneath the
Potomac River as well as the beaches of Nantucket Island. For his
experiment, Tuominen and colleague Derek Lovely, a UMass
microbiologist, created a tiny electrode and grew a biofilm of
bacteria around it. They were then able to measure its
conductivity by passing a current of electricity through the
electrode.

"These nanowire networks showed the same properties of metal
networks," Tuominen said. "We didn't think nature could make
something similar to metal. This is the first time this has been
discovered and this is very exciting for us."

Other experts in the field agree that the discovery is a big
deal. Stuart Lindsay, director of the Center for Single Molecule
Biophysics and the Biodesign Institute at Arizona State
University, called it "remarkable."

"It's a story that's been developing over years. These
measurements are beautiful. They tell you the proteins are
behaving like nanoscale wires. That is astounding."

Lindsay predicted that biological engineers could use the results
to build biological batteries more powerful than chemical ones.
He notes that existing batteries are constrained by the amount of
surface area on their electrodes. To generate a bigger charge,
you need a bigger battery. But the microscopic pili have a huge
amount of surface area that could be harnessed to create
electricity.

Tuominen adds that he believes these conducting bacteria could
also be used underwater, where the performance of typical
electronic materials is unsuitable.

"Water-based sensors and energy storage or energy conversion
devices are two possibilities, since this is a material that
clearly functions best in water," Tuominen said. "A big plus is
that these materials do not require any rare or expensive
feedstock materials. They will be cheap to produce because they
are nature designed and nature made."